Method of decorating glazed glass-ceramic bodies

ABSTRACT

THIS INVENTION RELATES TO THE STAIN COLORING OF GLAZED GLASS-CERAMIC ARTICLES, WHICH HAVE A CRYSTALLINE INTERLAYER BETWEEN THE GLASS-CERAMIC UNDERBODY AND THE GLAZE, BY AN ION EXCHANGE PROCESS WHEREIN SILVER AND/OR COPPER METAL COLORING IONS ARE EXCHANGED FOR ALKALI METAL IONS IN THE GLAZE, AND THE COLORS PRODUCED ARE RELATED TO THE ION EXCHANGE FIRING SCHEDULE, THE COMPOSITION OF THE STAINING PASTE, AND THE REFIRING SCHEDULE, IF ANY.

United States Patent 01 ice 3,583,883 METHOD OF DECORATING GLAZEDGLASS-CERAMIC BODIES Peter Grego and Robert G. Howell, Corning, N.Y.,assignors to Corning Glass Works, Corning, NY. No Drawing. Filed Jan. 6,1969, Ser. No. 789,375 Int. 'Cl. C03c 17/26 U.S. Cl. 117-123 8 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to the stain coloringof glazed glass-ceramic articles, which have a crystalline interlayerbetween the glassceramic underbody and the glaze, by an ion exchangeprocess wherein silver and/or copper metal coloring ions are exchangedfor alkali metal ions in the glaze, and the colors produced are relatedto the ion exchange firing schedule, the composition of the stainingpaste, and the refiring schedule, if any. i

BACKGROUND OF THE INVENTION The invention of glass-ceramic materials, asdisclosed in US. Pat. No. 2,920,971, provided a new family of materials;and US. Pat. No. 3,146,114 provided a new family of glass-ceramics inthe ternary system of which have been found to be particularly usefulfor dinnerware. It was also found that by glazing those glassceramicmaterials improved durability and strength could be provided. Suchglazes are disclosed in US. Pat. No. 3,384,508. That patent teaches thatglazes of a particular composition, when fired on the glass-ceramicbody, react and form a crystalline interlayer between the amorphousglaze and the glass-ceramic substrate. This crystalline interlayerextends into the glaze and the glassceramic substrate so as to provide astrong bond therebetween. By virtue of this interlayer, largedifferences in the coefiicient of expansion of the glaze and underbodycan be tolerated so as to allow high compressive stresses to bedeveloped in the glaze. .The glaze is essentially non-porous andamorphous, and consists essentially of,

Patented June 8, 1971 desirable properties could lead to porosity, ormicrochecks, in the surface of the body, which are a hazard to healthand sanitation since they can act as sites for bacteria growth.

Therefore, it was necessary to devise suitable techniques for decoratingglazed glass-ceramic articles.

SUMMARY OF THE INVENTION We have discovered that glazed glass-ceramicarticles having a crystalline interlayer can be stain-colored anddecorated by an ion exchange process wherein silver and/ or copper metalcoloring ions are exchanged for the alkali metal ions in the glaze. Thisprocess allows us to produce a variety of colors while maintaining thedesirable characteristics of the glazed glass-ceramic article. Moreover,it is believed that glazed articles without the crystalline interlayercannot be similarly stain-colored. Furthermore, we have discovered thatby particular heat treatments we can obtain a variety of colors. We havealso found that after certain colors have been developed they may bechanged by refiring the body at a temperature higher than the highestprior firing temperature. However, all glazes which produce thecrystalline interlayer cannot be used. Therefore, we have found that inaddition to the other compositional limitations the glaze must contain atotal of at least three percent by weight, K 0 and Na O.

DESCRIPTION OF THE PREFERRED EMBODIMENT The chemical composition of theunderbody, or glassceramic base, is not believed to have any effect uponthe stain-coloring of the glazed glass-ceramic article. Thus, asindicated in US. Pat. No. 3,384,508, any of the glassceramiccompositions disclosed in US. Pat. No. 2,920,971 or 3,146,114 may beutilized as underbodies. However, as disclosed in 3,146,114, it has beenfound that in the dinnerware field glass-ceramics wherein nepheline ispresent as one of the primary crystal phases, and especially wherenepheline and celsian together constitute the primary phases, are themost desirable bodies. The composition of several of the more desirablebodies are set forth below, in Table I, in weight percent.

TAB LE I on a weight percent basis, 1.516% Na O, 310% A1 0 4-19% B 040-70% SiO 08% K 0, 012% CaO, 0 40% PbO, 05% ZrO 05% CdO, 08.5% Cal-"02% ZnO and 09% MgO, with the total of the alkali metal oxides notexceeding 16%.

It is highly desirable to decorate these glazed glasscerarnic articlesso as to provide a more attractive appearance. The standard techniquesfor decorating glasses and/ or glass-ceramic articles are enameling,diffusing, and.

of expansion, or other properties. Certain of these uny We have foundthat the glaze composition must be within the range disclosed in US.Pat. No. 3,384,508. However, we have also found that the glaze mustcontain by weight, at least 3% K 0 and Na O otherwise the number ofalkali ions which exchange with the metal coloring ions are insufficientand little, if any, stain-cob oring will take place. Although Na O canbe as low as 1.5% we prefer to have at least 3% Na O in the glaze. Theglaze when fired and matured onto a glass-ceramic underbody apparentlyreacts with the body so as to produce a crystalline interlayer betweenthe glaze and underbody. The crystals of the interlayer extend into theunderbody and into the glaze. Normally, the matured glaze has athickness of from .004 to .010 inch. The composition efseverai flfil fterssie eze-slsstiqrtsleeni The mechanisrn by which this stain 'coloringofglazed glass-ceramics takes place is not completely understood.

ne. .11fld. .(u alth u h. h sulfate .9.h 9 ?5z a other similafcompoundsmay beTJsed. Whefithe sulfides are used, the silver sulfide is from 5.75to 80 weight percent and the copper sulfide is from 2.75 to 75 weightpercent of the total dry solids. The weight ratio silver sulfide tocopper sulfide is between about 1-:6 and 12:1, with the total amount-ofboth in the paste being between about 35 and 95% by weight. 1

Copper stains can produce, depending upon: treatment, red or yellowstain colors; On'theothefhand, coppersilver stains within theaforementioned ranges, can produce, depending upon treatment, amber,'blue or green colors. By refiring at a higher temperature the amber canbe changed to a blue or green and the blue can be changed to a green.The range of blue and green colors which can In lass there is asubstitution of one metal coloring ion I I for one alkali metal ion andas a result thereof a" color be i f accordlpg the system of center willform and grow to a particular size. The size 9 9 999F3 a C l i Accordingto of the color center will not yary significantly as a result h tsystem t gi yfihiw are K 5 5 5 of any post-ion exchange treatment of theglass, Inthe t tt 1? .F-l 0 T t y Xalues glazed glass-ceramic body it isbelieved that there is a a i ..fix}" m coemclents P fi m e maxlmumsubstitution of one metal coloring ion for one alkali metal t}? m'othellqoptdmate fll Q- Q ion as there is in glass. Howevenin' certainstaining-paste P 5 0119 1 and 'T 9 Q fi f g composition ranges, it isthought that the size of the color u nf s wherei'x 13 greater t 0 icenter changes with changes in the ion exchange firing than :2814 Wlth 3greater than 2753 and less 5.3 schedules and post-treatments of thebody. These changes 3 The -Q can defined as xhgrea-ter than areapparently related to the, crystalline interlayer but in and less than3550 h greater t an 3250 but what manner and to what extent is notpresently known. than The ambers whlch are produced have t 6 Variationin the ion exchange firing schedule and any color coordinates at greaterthan .4353 and less than .5039 firing of these particular stain-coloredglazes results in a wlthiy than-5363113141; less. h change in the color,which is believed to be related to a The Paste addlton h metal change inthe color center size. This color change is excompounds,also contam m Fl tremely unusual when it is considered that the glaze has clzers wattmgagentsi plasttclzers i mf an amorphous structure similar to that ofglass and that and wettmg agents F j amounts the stain-coloring takesplace entirely within the amorknown'to Q P P W i m the t: mak phousglaze structure and apparently not within the crysi Paste 9f h PrQPerV1S CS1tY for F B- YP talline interlayer. In glasses the intensity, butnot the 2 m f ji 9 and/or Color, can be varied with changes in the ionexchange hgnosulfonate; while -typ1cal= wettrngagents 1nclude lsofiringschedule and retiring. However, there is no change 91 e y a hol and/orwater. A1 0 is a in color in glasses as there can be in glazed glass-Preferred t' T 9%95 i my tPlckpesses ceramics. Thus, there are changeswhich can take place tw 9 "-O n -F atmg 1s less in stain-colored glazedglass-ceramics that do not take h 2 'Qifl 7 Stain begins become Pale Ifplace in staimcolored glasses greater than .005 of an 1nch,' the pasteleaves a hardmud We have found that when the crystalline interlayer is 9Fm on h Surface H should not present we cannot obtain particularfeatures of our p f f these are preferrved tanges'and not invention; asfor example when the glazes are applied to a s fi ?fi We flil to PQX thePaste metal substrates or to non-interlayer forming glass-cea h Othelfmethods 9 2vlPpllcaltyiowll' caflbe s ramic substrates. Thus, thosefeatures must be related to F e mp the Pf C n (1180 applied byflow/0621- the crystalline interlayer which has formed. The maxi- Iing', dipping, and jscreening. 'Table''IlI'below sets forth mum depth ofthe. stain-colored surface is approximately lZ diffe'rent stainingpastes which areexemplary'ofjth ose 40 microns and the glaze isapproximately,.004 to .010 whichmay be used. i

. TABLEIH 34.5 -6.'0 57.5 134.5 24.5 I 300 05.0 50.0v 40.0 3550-. 35.020.0 0.0 34.5 10.0 3.0 12.0 15.0 .300 45.0 21.0 32.0 60.0 75.0 00.5 00.532.5- 63.5 03.5 30.0 30.0 1.0 1 1.0 1.0- 1.0, 1.0 5.0,; 5 0 5.0 3.0 3.0.50 5.0 w t mnflu 150.0, 150.0 150,0 150.0, 150.0 in 50.0 v 50 0 50.0125.0 125. 0 125.0 7 125.0

inch thick. Thus it is apparent that the stain-coloring does Afterapplication the paste is dried so as to remove not extend into thecrystalline interlayer, 'so' that the water and any other volatileconstitutents before the 'ion phenomena is not believed to beexplainable by the stainexchange firing. Drying can be carried out attemperaing of the crystalline interlayer or other direct interaction 1'tures betweenroom temperature and about 120 C. for between the stainand interlayer. 1 times between about 10 and 30 minutes.

The staining paste of our invention contains silver con- The coated bodyis then heated to 'a temperature betaining compounds and/or coppercontaining compounds tween the lowest temperature at which a uniformion" exin a finely divided fluid media. The copper and silver conchangewill take place and the temperature atwhich the taining staining pasteshave been formulated so that the glaze will soften. We have found thatlittle, if any, ion silver content thereof is from'3.0 to 71.5 weightpercent, exchange is'elfected at temperatures less than 550 C. of thetotal dry solids, and the copper content thereof is and that if anyexchange is effected, it is non-uniform.

from 2 to 50 weight percent of to'taldry solids. In these pastes theweight ratio of silver to copper is between 1:4

and 15:1 with the total amount of copper and silver being between about25% and 80%. Normally, we prefer Perhaps atunreasonably lon'g'lengths oftime at temperatures below 550 C. a uniform exchange will take place.Above about 800 C. most of the glazes become softand begin to deform.Thus,800 C. isthe' maximum to use compounds such as silver sulfide (AgS) and coppractical firing temperature. The paste and body are held atthe particular ion exchange firing temperature for a sufficient lengthof time to affect the exchange; In most instances, that length of timeis between minutes and 2 hours depending on the color desired. At timesless than 5 minutes little, if any, stain coloring takes place whereasat times longer than 2 hours a hazy surface is developed. With all otherparameters held constant, ,vari ous colors can be produced by ionexchange firing the paste and body at different temperatures between 550and 800 C. The length of time of firing has less affect on the colorthan the change in temperature, but changes in time do affect the hue.Thus, in the copper-silver system by varying the ion exchange firingschedule, a variety of colors and hues can be produced.

The depth of the ion exchanged layer can vary from between about 1 to 50microns, depending upon treatment. In the copper-silver strains thereducing conditions within the glaze are sulficient to reduce themonovalent coloring ion to the metal ion. Thus, there is no need for thesubsequent conventional heat treatment to reduce the metal ion to anatom so as to produce a color. The colors which are produced by thistreatment are amber, blue, and green. When using only a copper stain itis necessary to utilize a reduction heat treatment in a mild reducingatmosphere such as sulfur dioxide or 20% hydrogen and nitrogen mixture.The colors produced with copper alone are yellow and red.

We have quite unexpectedly discovered by retiring the copper-silver ionexchanged body at a temperature greater than the highest prior firingtemperature a color change can be produced. In view of the experiencewith glass and the similarity between glasses and the glazes, theseresults are totally unexpected and unexplainable. In order to obtainthese color changes, the body must be fired at a temperature between 550and 800 C. for periods of time from 5 to 60 minutes, and at atemperature above the highest prior firing temperature. The colorproduced by the refire is similar to that color which could be producedif the body were originally ion exchanged at the refire temperature. Forexample, a green may be obtained by firing at 700 C. initially orthrough a series of firings up to 7 00 C. However, there may be a slightdifference between the colors produced by the different firings. Thelength of time necessary to affect the color change by refiring isusually shorter than that necessary if the body were originally ionexchanged at the same temperature. We have found there to be nolimitation as to the number of refirings that a body may be subjected toprovided, of course, the treatments meet the aforementioned limitations.It is theorized that these changes in color are produced by the changein size of the color center. However, the mechanism by which this colorcenter changes in size is not understood in view of the fact that thisglaze is so similar to a glass and this phenomena cannot be produced inglass, or in glazed bodies having no intermediate crystallineinterlayer. Thus, the only explanation can be the presence of thecrystalline interlayer.

In general, in the copper-silver staining system depending upon theexact composition of the paste, amber colors are produced by firing orrefiring between about 550 and 600 C. Blues can be produced 'in thesilver rich compositions between about 600 and 700 C. and greens betweenabout 700 and 800 C. in the copper rich copper-silver systems greens areproduced between about 600 and 800 C.

Our invention is further illustrated by the following examples:

Example I A glass-ceramic substrate was prepared by melting a glassbatch consisting essentially of, in weight percent on the oxide basis,43% SiO 30% A1 0 13.8% Na O, 5.6% BaO, 6.5% TIO2, and 0.9% AS203. Themelt was then formed into the shape of a dinner plate and then cerammed.A glaze of the following composition 47.6%

SiO 75%" A1 0 3.0% Na O, 9.7% B 0 0.5% F, 1.2% K 0, 8.2% CaO, 21.2% PbO,0.3% CdO, and 0.8% ZnO was prepared and fired onto the cerammed dinnerplate, thus forming a completed dinner plate. Next a high silver-lowcopper staining paste of the following composition was prepared 34.5grams Ag S, 6.0 grams 0118, 60.5 grams A1 0 1.0 gram bentonite and ml.water. This was ball milled into a sprayable slurry and sprayed onto theglazed plate and then allowed to air dry. The dry coated plate was thenion exchange fired in an air atmosphere in an electric furnace at 600 C.for 5 minutes. The plate was then cooled and the residue removed. Theplate was an amber color having the following color coordinates:x=0.4778, y=0.4268, and z=0.0954'.

Example II An amber stain colored body was prepared as in Example I.However, the body was refired at 650 C. for 30 minutes and the ambercolor was converted to a deep blue having the following colorcoordinates: x=0.2789, y=0.2'802, and z=0.4409.

'Example III Example 'IV The green stain colored body as produced inExample III was refired at 800 C. The resultant color was a light greenhaving the color coordinates of: x=0.3340, y=0.3709', and z=0.2950.

Example V A glazed glass-ceramic dinner plate was prepared as in ExampleI. A high copper-low silver staining paste of the following compositionwas prepared: 60 grams Ag S, 34.5 grams CuS, 60.5 grams A1 0 1.0 grambentonite and 150 ml. water. The paste was sprayed onto the body andallowed to air dry. The coated body was ion exchange fired at 550 C. for60 minutes. After cooling and cleaning, the body was found to have anamber color. The body was then refired at a temperature of 600 C. andwas found to have an olive green color having color coordinates of:x=0.3500, y=0.4200, and 2:0.2300.

Example VI A coated glazed glass-ceramic body as in Example V was ionexchange fired at 700 C. for 30 minutes. After cooling, the body wasfound to have a green color.

Example VII The amber stain colored body of Example V was refired at ahigh temperature of 750 C. The resultant color was a green.

Example VIII The stain colored body of 'Example VII was refired at ahigh temperature of 800 C. and was found to have a yellowish-greencolor.

Example -IX The paste was sprayed onto the body and allowed to'air dry.The coated body was fired in air at 650 C. for 15 minutes. After coolingand cleaning, the body was found to have a bright yellow color.

Example X The coated body of Example 1X was fired in a S0 atmosphere for30 minutes. After cleaning the stain color was a light yellow. Thebright yellow body was then retired in a 20% hydrogen-80% nitrogenatmosphere at 590 C. for 30 minutes. The resultant color was a brickred.

We claim:

1. A method of stain-coloring a glazed glass-ceramic article, having acrystalline interlayer, wherein said glaze consists essentially, on aweight percent basis, of 15-16% Na O, 3-10% A1 0 4-l9% B 0 4070% SiO 08%K 0, 0-12% CaO, 040% PbO, 0'-5% ZrO 0-5 CdO, 08.5% Cal- 0-2% ZnO and 09%MgO with the total of the alkali metal oxides not exceeding 16%, and thetotal of Na O and K 0 being greater than 3% comprising the steps of:

(A) coating the glazed surface with a staining paste containing bothcopper and silver coloring ions;

(B) heating the coated glazed surface to a temperature between 550 C.and 800 C., for a length of time sufficient to exchange the copper andsilver coloring ions with the alkali metal ions of the glaze.

2. The method of claim 1 wherein:

(A) the copper coloring ion comprises in Weightp'efcent, of thetotal drysolids, between 2 and"50% of the staining paste, and

(B) the silver coloring ion comprises in weight percent, of total drysolids, between 3.071.5% of the staining paste.

3. The method of claim 2 wherein the total amount of the metal coloringions is between about 25 and 80% by I 0 prior firing temperature andbetween S S O C. and 800 for alength of time'suflicient'twchangethecolordevelarticle is heated to a temperaturehigher than the highest color is green.

oped in the glass by the ion exchange.

5. A stain-colored glazedg'lass-ceramic article comprising aglass-ceramic underbody, a crystalline interlayer, and a glazeconsisting essentially on a weight percent basis of 15-16% Na O, 340% 10,, 4 19%'-B =o -,40-70% S10 0+s% 1 o, 0 12 'Caof,"0'- 40% PbO, 0 5% ZrO0-5% 'CdO,'0-8.5%'; CrF 0"-2% Z:nO"'and"0 9%' Mgo with the total of thealkali metaloxidesfnot exceeding 16% and the total of Na O and-K 0:being greater than 3%, and wherein the surface of said glaze containsboth copper and silver coloring'ions.

6. An article as recited in claim 5 wherein the staincolored surface isfrom 1'- to .50mic'rons thick.

7. An article asrecited in claim s wherein the stainql is 9 Y f 8. Anarticle 'a's recited in claim 5 whereinthe stain- UNITED STATES-PATENTS2,662,035 12/1953 Levi-' 106-'34X 3,079,264 10/1961 *GregotaLJ. '106-343,313,644 4/1967 Morr'issey 161'1X 3,384,508 5/1968 Boppetal. 117 123(A)3,419,370 12/1968 Crameretal 117-118X 3,420,698 1/1969 Smith 10634XALFRED L. LEAYITT, Primary Examiner W. F. CYRON, Assistant Examiner 1..U.S. 01x12. 117-124,-12s

